Method and apparatus for elimination of static disturbances



F. W. KRANZ Sept. 17, 1929.

l lETHOD AND APPARATUS FOR ELIMINATION OF STATIC DISTURBANCES Filed June 9, 1924 Patented Sept. 17, 1929 UNITED ST rnnnnmcrw. IKRANZ, or GENEVA, ILLINOIS, Assmivon re n comma, "'rnusrrnn METHOD AND APPARATUS FOR ELIMINATION a or s'rn mo" ms'rumnncns Application filedzJune 9, i924; :Serfitl No. #15363.

In the receptionkof radio messages, one of the chief sources of difliculty in securing properreceptionis the presence of electrical disturbances known as static, which cannot be eliminated by the simpleetuningof the usual receiving set.

it is an object of this invention to provide a method and apparatus whereby these dis- 'tur'bances may be eliminated or greatly minimized inthe receptionof radio messages.

It is a furthe'rfobject of this invention to "provide means for associating together two audion vacuum tubes such as are usual in radio receiving sets, and using them as detector, tubes in such a fashion thata voltage impressed upon them by an impulsei'rom the antenna willhaveflan equal eifectl'upon both of them, the output of such tubesfbeing so associated together and so connected in op- QO posingisenses with' the circuits of the subsequent apparatus that there will appear in said subsequent circuits noeffect of the impulses from the antenna itself.

It isa further object of this invention to provide means for connecting electrically with two detector tubes the'electrical oscillations from a (local source in a such a fashion that the resultingvoltageswill be impressed uponfltheogrids of the two .detector tubes equally, but in opposite phase. ,The resulting voltages or the same frequency as 1 these locally generated ioscillations,.as well as those of the interaction frequencies between the locally generated voltages and those received 7 from the antenna, which appear in the output, will ,be equal from thetwov tubes, and duetofthe arrangement of'the outputs in connection with the subsequent apparatus these voltages will be impressed upon said 40 apparatus.

It.1s also anobject of this invention to provide means for eliminating in a.- radio receiving. apparatus the direct effects of electrical impulses L from the ,antenna, but preserving 4 theinteraction eflects whichthese electrical impulses from ,the antennaihavewith locally controlled electrical; impulses.

It isi 'fi'nally an importantobject 015 this invention to provide a method andlapparatus o fthe class described, which' isada p'ted to permit of proper, signalreception andatf the same time to eliminate undesirable electrical disturbances. i l y i e The invention (in :a preferred form)fuis show'non the drawings and hereinafter more wfullyldescribed.' p

Onjtheldrawings: I

I Thefigure isa diagrammatic illustration of an electric circuit, embodying-the vprin- ,ciple's ofthis inventiong 'As shown on the drawings: a, 1

A circuitcontains two vacuum tubes i 1 and 2,1tvith a commonfilament' battery 3, one end oi whi hji connected withgroundatGyland [also through an inductance, coil [5 toan v an- E5 tenna 4, AI coil GconnectedWithSaid battery 3 .is ,inductiviely coupled to the (coil '5. Qne terminal of the 'coil'fi is connected to coils Fraud 8. at a commompoint; A, and the opposite ends of said coils;arevconnected by conductors '7 and 8 respectively to gr ids 11 (and 1 2 of gthe; tub'es {I and; 2 b respectively. tThe-coilszand. 8 are ofthesame dimensions, and are so that the. direction .of w ind M ing is the same in passing from a pointB .to ipoiatvA, asa-in passing from point A to pointf.v e c i v Said coils 7 andu8w'are ,ialsoa inductively coupled to a coil 9,}vfvhich.,.is}the, oscillation "coil o'fa circuit 'whi'ch alsocontains a-vacuum so r-tube 3, ,batteries 19; and\,20,1 and,.a(tuning condenser10. I i i The circuit mending an; detector ,tubes 1: and {2 is'complet'ed bygtwo equal coils or resistances 13 e and l iwhich are connected to the plates of said tubes, and at a commonppoint D to a t B. battery 22 The connection-[from the detector of hi i v n i to 2 1 3 1 amassin and amplifying apparatus and telephone re- 9 ceivers connected thereto, is made from the points B and C by conductors 17 and 18. The two detector tubes are thus in perfect symmetry with all other parts of the apparatus, with the exception of the direction of the inductive coupling between coil 9 and the coils 7 and 8.

It is a Well known characteristic of Vacuum tube circuits, especially when adjusted so that the tube functions particularly as a detector, that when two or more frequencies are impressed on the input, there will appear in the output not only the impressed frequencies, but also the octaves of these frequencies, as well as the sums and differences of the impressed frequencies;

Because of the symmetrical arrangement of the circuits of this invention, the electrical impulses impressed on the tubes by the antenna by means of the coils 5 and'6, will affect the two tubes equally so that these impulses will always cause equal potentials on the grids 11 and 12, and likewise the points B and C will have no difference of potential due to impulses or frequencies from the antenna. Therefore, the impulses or frequencies from the antenna will of themselves not cause a voltage to be impressed onthe output terminals 17 and 18 if the circuits and tubes are properly balanced and their direct effects will'consequently be eliminated. Be-

' oscillator.

cause of the relative direction of winding of the coils 7, 8 and 9, an altern'ating'current through the coil 9 will cause potential differences in the coils 7 and '8, such that, if point B is at a higher potential than the point A, then said point Ais at a higher potential than thepoint C, and by an equal amount. Thus, when the grid 11 has a positive' potential with respect to ground, the grid 12 will have a negative potential, and in the output of the tubes a potential, due to the impressed potential from'coil9, will appear across the conductors 17 and 18. Also,

the potentials of the sum and of the difference frequencies due to the interaction between frequencies from the antenna 4: by way of the coils 5 and 6, and those from the local oscillator by way of thecoils 9, 7 and 8, will appear across the conductors 17 and It will'thus appear that the direct effects of the voltages from the antenna are eliminated, while the signal effects or currents which it is desired to receive are'preserved by interaction with the frequency of the local If the .frequency of said local oscillator is properly related to that of the desired incoming signal frequencies, the interaction frequencies, usually the difference frequencies, will be those of the broadcasted signals or other signals which it is desired to receive. Only such static disturbances will be transmitted as have a frequency which I to give a frequency which will be transmitted by the apparatus attached to conductors 17 and 18, and it will be apparent that the ap paratus may be so adjusted that these are negligible The impedances 13 and 14: may be resistances with conductors 17 and 18 directly connected on, or they may be inductive impedances with 17 and 18 inductively coupled by a coil. The connection point D may be made variable, as an assistance in properly balancing the tubes and circuits.

The frequencies of the voltage produced by the interaction between the incoming signal and the local oscillator may be above the audible range, and the subsequent apparatus may then consist of amplifiers and another detector unit to produce the original audible sound desired. l q

I am aware that numerous details of constructionand arrangement of circuits may be varied through a wide range without departing from the principles of this invention, and I therefore do not purpose limiting the patent granted hereon otherwise than necessitated by the prior art.

I claim as my invention:

1. In a circuit of the class described, two similar vacuum tube detectors symmetrically arranged, a radio receiving circuit, a circuit including the grids of both of said tubes and I that frequencies intermediate between the received radio frequencies and audible frequencies will be produced by the interaction in the detector circuits between the said frequency of the oscillator and the said radio frequencies, an output circuit including the plates of both of said tubes and a pair of substantially electrically similar impedances connected to said plates and ,ata common point to the said vacuum tubes through a plate battery, means for varying the relative amounts of impedance connected to said plates, and suitable receiving means connected to said impedances.

2. In a radio telephone receiving apparatus in combination, a local oscillator circuit set to a frequency appreciably removed from the carrier frequency, an antenna, a balanced detector circuit connected to said antenna and inductively coupled to said local oscillator circuit whereby the outputfrom the detector circuit will contain the frequency of an interval between the carrier frequency andthe local oscillator frequency with speech impressed side bands on either side, and an amplifying and detector circuit connected to the output of said balanced detector circuit.

3. Ina radio telephone receiving apparatus in combination, a local oscillator circuitv 

